So the Queen made clear last week that she is not going to abdicate, but will continue "to serve the people of this great nation of ours to the best of my ability through the changing times ahead". This means, of course, that Prince Charles will have to keep himself busy and useful in whatever ways he can until the summons comes, if it ever does, for him to claim his birthright.

I am pleased to read that to his already bulging portfolio of interests he has just added a new one: the manufacture of organic ice cream. But will even this be enough to keep him happy? Is it heartless of the Queen to condemn her eldest son (already 53, with a boy at university) to yet more years of frustration? What explains her reluctance, at the age of 76, to give up a job she has already been doing for half a century?

Some people may think she is being very selfish. They may think she is being like the president of Zimbabwe, Robert Mugabe, who, two years older than her, still clings desperately to office. They may take the view that nobody should do any job for too long, that everyone gets bored and stale in the end, and that, in any case, it is the duty of people of a certain age to pack it all in and make way for the next generation.

There are many examples in history of the damage caused by the refusal of the old to retire. Winston Churchill was 81 before he would agree to hand over the premiership to Anthony Eden, who by then had become so screwed up that he proved a disastrous prime minister. Charles de Gaulle should have left the Elysée palace much earlier than he did, in a dignified manner, instead of going bitterly into retirement at 79, only to die the following year.

And today we have two leaders, both in their 70s, who must take much of the blame for the mayhem and misery that disfigures the Middle East. It is hard to hold out any hope of an end to the Israeli-Palestinian conflict so long as Yasser Arafat and Ariel Sharon hang on to power.

But there are certain jobs in which age is a real asset - jobs in which continuity, experience, and wisdom (or, at any rate, the appearance of wisdom) are much more important than energy and competence at running things. These are jobs that rely on moral authority, and are often linked to the idea of lifelong sacrifice and service. The holder of one such job is Pope John Paul II. He may be 81, a victim of Parkinson's disease, and visibly ailing; but it is generally accepted that he should carry on until he dies, unless he becomes completely incapacitated.

Popes are not supposed to be quitters. Nor are British monarchs. The abdication of Edward VIII in 1936 plunged the monarchy into crisis and permanently damaged the ex-king's reputation in the eyes of his subjects. It took a world war and a noble younger brother to restore the monarchy's prestige. Now it is recovering from another rocky period.

If the prospect of Britain becoming a republic is now receding into the distance, it is not only because the royal scandals of the 1990s are beginning to be forgotten, and because the death of the Queen Mother has reminded people of a golden era of the monarchy. It is also because, by simply reigning and reigning, the Queen is adding all the time to her personal authority and strengthening her claim to represent continuity in a frightening, unpredictable world.

As William Shawcross' BBC1 series on the monarchy is showing, there is something mesmeric, even awesome, about the same individual performing the same routine constitutional functions - opening parliament, conducting investitures, etc - year after year, the only changes over the decades being the gradual lowering of her vocal register and the bulking out of her tiny frame.

Even convinced republicans in the press have confessed to becoming weak-kneed and tongue-tied when they actually met the Queen at a reception for the media at Windsor Castle. You can now sense that, after 10 pretty ghastly years, the Queen is regaining confidence once more in the power of the royal magic.

The time may still come when Britain settles for a republic, though this could probably only happen after a major political earthquake of some kind. In the meantime, the monarchy seems likely to grow in popular support so long as the Queen stays on the throne and Prince Charles contents himself with a supporting role.